This is a common misperception. The "medical redshirt" is/was the ability to apply to use your
one redshirt season for a season in which you already played, but played less than 1/3 of the season due to injury. This was basically made defunct by the new 4 game redshirt rule. There is no such thing as a
second red shirt year.
After he has exhausted his eligibility, he could petition for a "medical hardship waiver" to extend his eligibility an additional year. These are commonly granted if the circumstances meet basic criteria. i.e. a documented injury during competition forcing the player to miss more than 2/3 of one of their 4 seasons of eligibility.
However, a student athlete has a 5 year window in which to use their 4 seasons of eligibility**. So, Lucas (GT on his behalf) would have to apply for a medical hardship waiver
and a waiver of the five year clock. There is no NCAA rule governing this. It is a waiver of NCAA rules granted by the committee on a case-by-case basis. Usually a player only can get this if they miss
two seasons due to reasons "
beyond their control". Since Lucas previously 'voluntarily' red shirted, an additional season is unlikely to be granted. Ken S had a decent write up on this related to Tim Byerly after 2015*** (His waiver was denied, in a similar situation to LJ's)
Also, this could only happen after completion of his final season. He'd have to remain in school for an indefinite period to wait for the NCAA to decide if he can have a sixth year. A lot of players decide 5 years is enough and they don't want to hang around in limbo waiting for the NCAA to decide their fate.
Decent (though unofficial) summary of the rules:
https://www.athleticscholarships.net/2012/07/17/how-get-medical-redshirt.htm
**Division I five-year clock definition from the NCAA:
http://www.ncaa.org/student-athletes/current/transfer-terms
***
https://www.myajc.com/blog/georgia-...byerly-waiver-process/fdOc8otE6TpW5gmcH1XvrJ/